std::tuple_size<std::pair> (3) - Linux Manuals

std::tuple_size<std::pair>: std::tuple_size<std::pair>

NAME

std::tuple_size<std::pair> - std::tuple_size<std::pair>

Synopsis

Defined in header <utility>
template< class T1, class T2 > (since C++11)
struct tuple_size<std::pair<T1, T2>>; (until C++14)
template <class T1, class T2>
struct tuple_size<std::pair<T1, T2>> (since C++14)
: std::integral_constant<std::size_t, 2> { };

The partial specialization of std::tuple_size for pairs provides a compile-time way to obtain the number of elements in a pair, which is always 2, using tuple-like syntax.

Inherited from std::integral_constant

Member constants

value the constant value 2
         (public static member constant)
[static]

Member functions

                     converts the object to std::size_t, returns value
operator std::size_t (public member function)

operator() returns value
                     (public member function)
(C++14)

Member types

Type Definition
value_type std::size_t
type std::integral_constant<std::size_t, value>

Example

// Run this code

  #include <iostream>
  #include <utility>
  #include <tuple>

  template<class T>
  void test(T t)
  {
      int a[std::tuple_size<T>::value]; // can be used at compile time
      std::cout << std::tuple_size<T>::value << '\n'; // or at run time
  }

  int main()
  {
      test(std::make_tuple(1, 2, 3.14));
      test(std::make_pair(1, 3.14));
  }

Output:

  3
  2